Method for transferring micro device

ABSTRACT

A method for transferring a micro device is provided. The method includes: preparing a carrier substrate with the micro device thereon, wherein an adhesive layer is between and in contact with the carrier substrate and the micro device; picking up the micro-device from the carrier substrate by a transfer head; forming a liquid layer on a receiving substrate; and placing the micro device over the receiving substrate by the transfer head such that the micro device is in contact with the liquid layer and is gripped by a capillary force; and moving the transfer head away from the receiving substrate such that the micro device is detached from the transfer head and is stuck to the receiving substrate.

RELATED APPLICATIONS

The present application is a continuation-in-part application of U.S.application Ser. No. 15/896,007, filed Feb. 13, 2018, which is hereinincorporated by reference.

BACKGROUND Field of Invention

The present disclosure relates to a method for transferring a microdevice from a carrier substrate to a receiving substrate.

Description of Related Art

The statements in this section merely provide background informationrelated to the present disclosure and do not necessarily constituteprior art.

Traditional technologies for transferring of devices include transfer bywafer bonding from a transfer wafer to a receiving substrate. One suchimplementation is “direct bonding” involving one bonding step of anarray of devices from a transfer wafer to a receiving substrate,followed by removal of the transfer wafer. Another such implementationis “indirect bonding” which involves two bonding/de-bonding steps. Inindirect bonding, a transfer head may pick up an array of devices from adonor substrate, and then bond the array of devices to a receivingsubstrate, followed by removal of the transfer head.

SUMMARY

According to some embodiments of the present disclosure, a method fortransferring a micro device is provided. The method includes: preparinga carrier substrate with the micro device thereon, wherein an adhesivelayer is between and in contact with the carrier substrate and the microdevice; picking up the micro-device from the carrier substrate by atransfer head; forming a liquid layer on a receiving substrate; placingthe micro device over the receiving substrate by the transfer head suchthat the micro device is in contact with the liquid layer and is grippedby a capillary force; and moving the transfer head away from thereceiving substrate such that the micro device is detached from thetransfer head and is stuck to the receiving substrate.

It is to be understood that both the foregoing general description andthe following detailed description are by examples, and are intended toprovide further explanation of the disclosure as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure can be more fully understood by reading the followingdetailed description of the embodiment, with reference made to theaccompanying drawings as follows:

FIG. 1 is a flow chart of a method for transferring a micro device froma carrier substrate to a receiving substrate in some embodiments of thepresent disclosure;

FIG. 2 is a schematic cross-sectional view of an intermediate step ofthe method for transferring the micro device in some embodiments of thepresent disclosure;

FIG. 3 is a schematic cross-sectional view of an intermediate step ofthe method for transferring the micro device in some embodiments of thepresent disclosure;

FIG. 4A is a schematic cross-sectional view of an intermediate step ofthe method for transferring the micro device in some embodiments of thepresent disclosure;

FIG. 4B is a schematic cross-sectional view of an intermediate step ofthe method for transferring the micro device in some embodiments of thepresent disclosure;

FIG. 5A is a schematic cross-sectional view of an intermediate step ofthe method for transferring the micro device in some embodiments of thepresent disclosure;

FIG. 5B is a schematic cross-sectional view of an intermediate step ofthe method for transferring the micro device in some embodiments of thepresent disclosure;

FIG. 6 is a schematic cross-sectional view of an intermediate step ofthe method for transferring the micro device in some embodiments of thepresent disclosure;

FIG. 7A is a schematic cross-sectional view of an intermediate step ofthe method for transferring the micro device in some embodiments of thepresent disclosure; and

FIG. 7B is a schematic cross-sectional view of an intermediate step ofthe method for transferring the micro device in some embodiments of thepresent disclosure.

DETAILED DESCRIPTION

Reference will now be made in detail to the present embodiments of thedisclosure, examples of which are illustrated in the accompanyingdrawings. Wherever possible, the same reference numbers are used in thedrawings and the description to refer to the same or like parts.

In various embodiments, description is made with reference to figures.However, certain embodiments may be practiced without one or more ofthese specific details, or in combination with other known methods andconfigurations. In the following description, numerous specific detailsare set forth, such as specific configurations, dimensions andprocesses, etc., in order to provide a thorough understanding of thepresent disclosure. In other instances, well-known semiconductorprocesses and manufacturing techniques have not been described inparticular detail in order to not unnecessarily obscure the presentdisclosure. Reference throughout this specification to “one embodiment,”“an embodiment” or the like means that a particular feature, structure,configuration, or characteristic described in connection with theembodiment is included in at least one embodiment of the disclosure.Thus, the appearances of the phrase “in one embodiment,” “in anembodiment” or the like in various places throughout this specificationare not necessarily referring to the same embodiment of the disclosure.Furthermore, the particular features, structures, configurations, orcharacteristics may be combined in any suitable manner in one or moreembodiments.

The terms “over,” “to,” “between” and “on” as used herein may refer to arelative position of one layer with respect to other layers. One layer“over” or “on” another layer or bonded “to” another layer may bedirectly in contact with the other layer or may have one or moreintervening layers. One layer “between” layers may be directly incontact with the layers or may have one or more intervening layers.

FIG. 1 is a flow chart of a method for transferring a micro device froma carrier substrate to a receiving substrate. FIGS. 2 to 7B areschematic cross-sectional views of intermediate steps of the method 100of FIG. 1. References are made to FIGS. 1 to 7B. The method 100 beginswith operation 110 in which a carrier substrate 210 is prepared with amicro device 220 thereon. An adhesive layer 230 is between and incontact with the carrier substrate 210 and the micro device 220 (asreferred to FIG. 2). The method 100 continues with operation 120 inwhich the micro device 220 is picked up from the carrier substrate 210by a transfer head 240 (as referred to FIG. 3). The method 100 continueswith operations 130 and 140 in which a liquid layer 250 or a patternedliquid layer 250 is formed on a receiving substrate 260 (as referred toFIGS. 4A and 4B), and then the micro device 220 which has been picked upis placed over the receiving substrate 260 by the transfer head 240,such that the micro device 220 is in contact with the liquid layer 250and is gripped by a capillary force produced by the liquid layer 250 (asreferred to FIGS. 5A, 5B, and 6). The method 100 continues withoperation 150 in which the transfer head 240 is moved away from thereceiving substrate 260 such that the micro device 220 is detached fromthe transfer head 240 and is stuck to the receiving substrate 260 (asreferred to FIGS. 7A and 7B).

Although in the previous paragraph and FIG. 1 only “a” micro device 220is mentioned, “multiple” micro devices 220 may be used in practicalapplications and is still within the scope of the present disclosure, aswill be illustrated in the following embodiments.

Reference is made to FIG. 2. As mentioned above, the adhesive layer 230is between the carrier substrate 210 and a plurality of micro devices220. Specifically, the adhesive layer 230 is in contact with the carriersubstrate 210 and the micro devices 220. In some embodiments, theformation of the adhesive layer 230 is performed by coating an adhesivecapable material onto the carrier substrate 210. The adhesive layer 230may be coated by a spin coater, a slit coater, or any combinationthereof. In some embodiments, the adhesive layer 230 may be made of anadhesion capable organic material, such as epoxy, polymethylmethacrylate(PMMA), polysiloxanes, silicone, or any combination thereof.Furthermore, the adhesive layer 230 may have a thickness in a range fromabout 1 μm to about 100 μm.

An adhesive force F1 is an adhesive force of the adhesive layer 230 toeach of the micro devices 220, and has a value F11. In some embodiments,The adhesive force F1 is the adhesive force of the adhesive layer 230 toeach of the micro devices 220 after reduction, and has a value F12. Insome embodiments, the value F11, which is a value of the adhesive forceF1 without said reduction, is greater than the value F12. Said reductionis reducing an original adhesive force of the adhesive layer 230 to eachof the micro devices 220, which may be performed before some of themicro devices 220 are picked up. In some embodiments, the reduction maybe performed by heating, cooling, applying an electric field, anelectromagnetic radiation, ultrasound, a mechanical force, a pressure,or any combination thereof on the adhesive layer 230, and should not belimited thereto. In some embodiments, a lateral length L of one of themicro devices 220 is about less than or equal to about 50 μm. Saidlateral length is measured in a direction Y. The direction Y isperpendicular to a thickness direction Z, and the thickness direction Zis perpendicular to a planar extension direction of the carriersubstrate 210. For example, for one micro device 220 with a surface areaabout 10 μm×10 μm, said reduced adhesive force F1 has the value F12about 50 nanonewton (nN). Embodiments of this disclosure are not limitedthereto. Proper modifications to the adhesive layer 230 depending on anactual application may be performed. The adhesive force F1 may includevan der Waals forces, but should not be limited thereto.

In some embodiments, the carrier substrate 210 may be a rigid substrate.The rigid substrate may be made of glass, quartz, silicon, polycarbonate(PC), acrylonitrile butadiene styrene (ABS), or any combination thereof.Embodiments of this disclosure are not limited thereto. Propermodifications to the carrier substrate 210 depending on an actualapplication may be performed.

In some embodiments, the micro devices 220 may be a light emittingstructure such as a compound semiconductor having a bandgapcorresponding to a specific region in the spectrum. For example, thelight emitting structure may include one or more layers based on II-VImaterials (e.g. ZnSe, ZnO) or III-V nitride materials (e.g. GaN, AlN,InN, InGaN, GaP, AlInGaP, AlGaAs or alloys thereof). In some otherembodiments, the micro devices 220 may also be integrated circuits (IC)or microelectromechanical system (MEMS) devices, and should not belimited thereto.

Reference is made to FIG. 3. As mentioned above, some of the microdevices 220 are picked up from the carrier substrate 210 by the transferhead 240. In some embodiments, the transfer head 240 may exert apicking-up pressure or a picking-up force on each of the micro devices220 by way of, for example, vacuum, adhesion, magnetic attraction,electrostatic attraction, or the like. Hereinafter only adhesive forcewill be discussed, but other types of forces mentioned above are stillwithin the scope of the present disclosure. In some embodiments, thetransfer head 240 may have a plurality of grip regions 242 for pickingup and placing the micro devices 220. There may also be recesses 244among the grip regions 242 configured as a place accommodating objectsnot to be picked up and/or placed. Besides, when performing the placingof the micro devices 220 on the receiving substrate 260, objects thatare originally on the receiving substrate 260 will not be interfered.There may also be recesses 244 among the grip regions 242. The gripregions 242 of the transfer head 240 may be made of an adhesion capablematerial or, the transfer head 240 may have a patterned adhesive layerthereon, such that when the transfer head 240 is in contact with themicro devices 220, each of the micro devices 220 may be picked up by anadhesive force F2. In some embodiments, for one micro device 220 with asurface area about 10 μm×10 μm, said adhesive force F2 is about 100 nNto 1000 nN for one micro device 220. The adhesive force F2 may includevan der Waals forces, but should not be limited thereto.

As mentioned above, in some embodiments, the original adhesive force F1with the value F11 may be reduced before the picking up to form theadhesive force F1 with the value F12, so that a difference between theadhesive force F2 and the adhesive force F1 is increased so as tofacilitate the performance of picking up the micro devices 220.

Reference is made to FIGS. 4A and 4B. As mentioned above, the liquidlayer 250 is formed on the receiving substrate 260. The liquid layer 250may be formed as one layer on the receiving substrate 260 as shown inFIG. 4A or patterned to be discrete portions on the receiving substrate260 as shown in FIG. 4B. In FIG. 4B the patterned liquid layer 250 canbe where the micro devices 220 will be placed over. The receivingsubstrate 260 can be a display substrate, a lighting substrate, asubstrate with functional devices such as transistors or integratedcircuits, or a substrate with metal redistribution lines, but should notbe limited thereto. In some embodiments, the liquid layer 250 may beformed by lowering a temperature of the receiving substrate 260 in anenvironment including a vapor, such that at least a part of the vapor iscondensed to form the liquid layer 250 on the receiving substrate 260.Specifically, the liquid layer 250 or the patterned liquid layer 250 maybe formed on conductive pads 262 of the receiving substrate 260, butshould not be limited thereto. In some embodiments, an area of each ofthe conductive pad 262 is smaller than or equal to about 1 millimetersquare. In some embodiments, the temperature of the receiving substrate260 is lowered to about dew point, such that the water vapor in theenvironment is condensed to form liquid water serving as the liquidlayer 250. Furthermore, the formation of the liquid layer 250 may alsobe achieved by showering a vapor, inkjet printing, roller coating, dipcoating, or the like.

References are made to FIGS. 5A, 5B and 6. As mentioned above, the microdevices 220 which have been picked up are placed over the receivingsubstrate 260 by the transfer head 240, such that each of the microdevices 220 is in contact with the liquid layer 250 and gripped by acapillary force F31. Specifically, the micro devices 220 are placed inclose proximity to the conductive pads 262, such that the liquid layer250 can grip the micro devices 220. The meniscuses 252 of the liquidlayer 250 as shown in FIG. 6 are caused by the capillary force F31. Themicro devices 220 are gripped by the capillary force F31 produced by theliquid layer 250 between the micro devices 220 and the conductive pad262. In some embodiments, a thickness of the liquid layer 250 is lessthan a thickness of the micro devices 220 when the micro devices 220 aregripped by the capillary force F31. It is noted that a sequence ofoperation 130 and operation 140 can be exchanged. That is, the microdevices 220 can be placed onto and in contact with the conductive pads262 and then the liquid layer 250 is formed on the receiving substrate260.

Reference is made to FIGS. 7A and 7B. As mentioned above, the microdevices 220 are detached from the transfer head 240 after the microdevices 220 are gripped by the capillary force F31. In some embodiments,the micro devices 220 are adhered to the adhesive layer 230 by anadhesive force F1 with the value F11 or the value F12 as mentionedabove. Some of the micro devices 220 are attached to the transfer head240 by the adhesive force F2, and the capillary force F31 is greaterthan the adhesive force F2 such that the micro devices 220 are detachedfrom the transfer head 240 and are stuck to the receiving substrate 260when the transfer head 240 is moved away the receiving substrate 260after said placing as illustrated by in FIG. 7A.

In some embodiments, the method 100 further includes evaporating theliquid layer 250 such that at least one of the micro devices 220 isbound to one of the conductive pads 262 and is in electrical contactwith the conductive pad 262. The evaporation of the liquid layer 250 maybe achieved by, for example, raising a temperature of the receivingsubstrate 260 or the conductive pads 262. The micro devices 220 may haveelectrodes thereon respectively for electrically contacting theconductive pads 262. In some embodiments, the transfer head 240 is movedaway from the receiving substrate 260 before the liquid layer 250 isevaporated. Under this circumstance, a force F3 for overcoming theadhesive force F2 is the capillary force F31 as mentioned above, and thecapillary force F31 is greater than the adhesive force F2. In someembodiments, the transfer head 240 is moved away from the receivingsubstrate 260 after the liquid layer 250 is evaporated. Under thiscircumstance, the force F3 for overcoming the adhesive force F2 is asticking force F32 between one of the micro devices 220 and one of theconductive pads 262 produced after said evaporation, and the stickingforce F32 is greater than the adhesive force F2.

In some embodiments, the method 100 further includes lowering thetemperature of the receiving substrate 260 or the conductive pad 262such that the liquid layer 250 is frozen before the transfer head 240 ismoved away from the receiving substrate 210 as mentioned above. When theliquid layer 250 is frozen, another grip force F33 produced by thefrozen liquid layer 250 is applied to the micro devices 220. Generally,the grip force F33 is greater than the grip force F2.

In some embodiments, a combination of the transfer head 240, the microdevices 220, the liquid layer 250, and the receiving substrate 260 isheated to form a bonding between the micro devices 220 and the receivingsubstrate 260 via a bonding force F34 therebetween before the transferhead 240 is moved away from the receiving substrate 260. The bondingforce F34 is greater than the grip force F2.

In short, the force F3 includes one of the following forces: (1) thecapillary force F31 produced by the liquid layer 250 between the microdevices 220 and the conductive pads 262; (2) the sticking force F32between the micro devices 220 and the conductive pads 262 in which adifference between (1) and (2) depends on whether the liquid layer 250is evaporated; (3) the grip force F33 produced by the frozen liquidlayer 250; and (4) the bonding force F34 between the micro devices 220and the receiving substrate 260 after heating.

In some embodiments, lateral lengths of the micro devices 220 are lessthan or equal to 50 μm. The limitation on the lateral lengths is toensure feasibility of the above embodiments because some forces such asthe capillary force F31 caused by the liquid layer 250, the stickingforce F32 caused by interfaces between the micro devices 220 and theconducive pads 262 after evaporating the liquid layer 250 therebetween,and the grip force F33 caused by the frozen liquid layer 250 may begreatly changed according to the lateral lengths of the micro devices220. It is noted that an influence of the capillary force F31, thesticking force F32, and the grip force F33 on the micro devices 220 willgradually dominate other forces applied to the micro devices 220 whensizes (e.g., the lateral lengths) of the micro devices 220 graduallyscale down. Besides, gravitational forces need to be considered if thelateral lengths of the micro devices 220 are too great, which is notdesirable for implementing some embodiments disclosed in the presentdisclosure. In the above embodiments, at least one of the capillaryforce F31, the sticking force F32, and the grip force F33 is greaterthan the adhesive force F2 due to a size effect (i.e., smaller laterallengths) of the micro devices 220.

More specifically, the forces applied to the micro devices 220 with thelateral length within the range mentioned in these embodiments will obeyone of the following inequalities:

F11<F2<F31  (1)

F11<F2<F32  (2)

F11<F2<F33  (3)

F11<F2<F34  (4)

F12<F2<F31  (5)

F12<F2<F32  (6)

F12<F2<F33  (7)

F12<F2<F34  (8)

wherein the left-hand side of inequalities (1) to (8): F11<F2 and F12<F2may be satisfied by choosing suitable combination of materials for theadhesive layer 230 and surfaces of the grip regions 242 in contact withthe micro devices 220.

Table 1 lists various forces mentioned heretofore:

TABLE 1 Sym- bols Meaning F1 adhesive force of the adhesive layer 230 tothe micro device 220 F11 F1 without reducing an original adhesive forceof the adhesive layer 230 F12 F1 after reducing the original adhesiveforce of the adhesive layer 230 F2 adhesive force exerted by thetransfer head 240 to the micro device 220 F3 a force attaching the microdevice 220 to the receiving substrate 260 F31 a capillary force producedby the liquid layer 250 F32 a sticking force between the micro device220 and the conductive pad 262 produced after evaporating the liquidlayer 250 F33 a grip force produced by the frozen liquid layer 250 F34 abonding force after the formation of bonding between the micro device220 and the receiving substrate 260

Generally, the adhesive forces F1 (including the value F11 and the valueF12) and the adhesive force F2 per unit area do not change when laterallengths of the micro devices 220 are changed. In some embodiments, theadhesive force F2 may be additionally modified by the speed of moving upthe transfer head 240 away from the carrier substrate 210 after thetransfer head 240 is in contact with the micro devices 220. The fasterthe speed is, the greater the adhesive force F2 is. As such, transferprocesses mentioned above may be achieved with adhesive type transferhead 240. Complicated circuit designs or mechanical designs for transferheads operated by electrostatics force, vacuum force, mechanical force,or any combination thereof can be omitted. An adhesive type transferhead 240 is capable of completing the transfer processes, and the costof the processes is reduced.

In the above embodiments supported by FIGS. 1 to 7B, after some of themicro devices 220 are placed over the receiving substrate 260, the microdevices 220 are gripped by the capillary force F31 produced by theliquid layer 250 between the micro devices 220 and the conductive pads262, the sticking force F32 between the micro devices 220 and theconductive pads 262 produced after said evaporating, the grip force F33produced by the frozen liquid layer 250, and/or the bonding force F34after the combination of the transfer head, the micro device, the liquidlayer, and the receiving substrate are heated to form the bondingbetween the micro devices 220 and the receiving substrate 260, and thenthe micro devices 220 are detached from the transfer head 240 and beingtransferred to the receiving substrate 260. As such, an adhesive typetransfer head 240 without complicated circuit design is capable ofcompleting the transfer processes due to the presence of the liquidlayer 250, and the cost of the processes are reduced.

In summary, a method for transferring a micro device from a carriersubstrate to a receiving substrate by an adhesive type transfer head isprovided. As such, the transfer process is simplified by a simplemechanism of transferreing.

Although the present disclosure has been described in considerabledetail with reference to certain embodiments thereof, other embodimentsare possible. Therefore, the spirit and scope of the appended claimsshould not be limited to the description of the embodiments containedherein.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the method and the structureof the present disclosure without departing from the scope or spirit ofthe disclosure. In view of the foregoing, it is intended that thepresent disclosure cover modifications and variations of this disclosureprovided they fall within the scope of the following claims.

What is claimed is:
 1. A method for transferring a micro device,comprising: preparing a carrier substrate with the micro device thereon,wherein an adhesive layer is between and in contact with the carriersubstrate and the micro device; picking up the micro device from thecarrier substrate by a transfer head; forming a liquid layer on areceiving substrate; placing the micro device over the receivingsubstrate by the transfer head such that the micro device is in contactwith the liquid layer and is gripped by a capillary force; and movingthe transfer head away from the receiving substrate such that the microdevice is detached from the transfer head and is stuck to the receivingsubstrate.
 2. The method of claim 1, wherein the micro device is adheredto the adhesive layer by a first adhesive force, the micro device isattached to the transfer head by a second adhesive force, and thecapillary force is greater than the first adhesive force and the secondadhesive force such that the micro device is detached from the transferhead and is stuck to the receiving substrate when the placing isperformed.
 3. The method of claim 2, wherein the first adhesive forceand the second adhesive force comprise van der Waals forces.
 4. Themethod of claim 2, wherein the second adhesive force is greater than thefirst adhesive force.
 5. The method of claim 1, wherein a lateral lengthof the micro device is less than or equal to 50 μm.
 6. The method ofclaim 1, wherein a photoresist layer is on the micro device before thepicking up, and the micro device is attached to the transfer head viathe photoresist layer when the picking up is performed.
 7. The method ofclaim 6, wherein the micro device is adhered to the adhesive layer by afirst adhesive force, the micro device is attached to the transfer headvia the photoresist layer by a third adhesive force, and the capillaryforce is greater than the first adhesive force and the third adhesiveforce such that the micro device is detached from the transfer head andis stuck to the receiving substrate when the placing is performed. 8.The method of claim 1, further comprising: evaporating the liquid layersuch that the micro device is bound to a conductive pad of the receivingsubstrate and is in electrical contact with the conductive pad beforethe micro device is detached from the transfer head, wherein a forceattaching the micro device to the conductive pad is a sticking forceproduced after said evaporating.
 9. The method of claim 8, wherein themicro device comprises an electrode thereon, and the micro device isbound to and in electrical contact with the conductive pad via anelectrode.
 10. The method of claim 8, wherein the micro device isadhered to the adhesive layer by a first adhesive force, the microdevice is attached to the transfer head by a second adhesive force, andthe sticking force is greater than the first adhesive force and thesecond adhesive force such that the micro device is detached from thetransfer head and is stuck to the receiving substrate when the placingis performed.
 11. The method of claim 8, wherein an area of theconductive pad is smaller than or equal to about 1 millimeter square.12. The method of claim 1, further comprising lowering a temperature ofthe receiving substrate such that the liquid layer is frozen beforemoving the transfer head away from the receiving substrate.
 13. Themethod of claim 1, further comprising: heating a combination of thetransfer head, the micro device, the liquid layer, and the receivingsubstrate to form a bonding between the micro device and the receivingsubstrate via a bonding force therebetween before the transfer head ismoved away from the receiving substrate.